Questions tagged [apu]

Auxiliary Power Unit. A device for providing alternate power to an aircraft, usually located in the aircraft's tail.

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What is this device protruding from the rear of this 787?

While looking at the photos from this question I noticed a small protrusion from the side of the plane. You can see it in the photo: and in the diagram from l@aeroalias answer: In the diagram it ...
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In what conditions is the APU used in midair?

In flight, engines provide all the needed energy (bleed air, hydraulic and electrical power). So the APU can be shut down shortly after engines are running. But I imagine that starting the APU in ...
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Was the miracle on the Hudson saved exclusively by the APU?

In the film Sully, (staring Tom Hanks) the APU is switched on straight after both engines rollback, why was this step necessary; Airbus said this was the "15th thing" to do on the checklist. How or ...
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Why can't we use APU bleed air for wing anti ice on the A320?

The question says it all. While reading I came across this that we can under no circumstances use APU bleed air for supplying wing anti ice? Any reason?
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How are APUs started?

How are jet engines started? says that engines must be started from bleed air, which can come from the APU, another engine, or a huffer cart, or from windmilling. As far as I understand, APUs are ...
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Why is the APU located in the tail for almost all commercial aircraft?

I know there are planes whose APU (Auxiliary Power Unit) is located elsewhere, but for the most common commercial jet aircraft (A320, B737, B747, A330,...), the APU is located in the tail. Is there a ...
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Can the APU provide emergency thrust?

By David Monniaux (Own work) [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.0 fr], via Wikimedia Commons Many larger airplanes have gas turbine APUs (auxiliary power units). It seems that their exhaust is ...
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What is the APU actually used for?

What are the actual uses of the APU? When is it used? When does it go off?
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Why is the 787 tail cone made out of titanium?

In this question there is a drawing of a 787 that shows that the tail cone is made of titanium. Why is such a heavy-duty material like titanium required for the tail cone? I do not see how there ...
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Why isn't the APU a standard diesel generator?

Why isn't the APU a standard diesel generator? Jet-A and diesel are interchangeable (with the addition of a lubricant). So why not use a cheaper piston engine as opposed to a jet turbine? V.S.
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Where is the APU in the case of an S-duct (like the L-1011)?

This question asks about the S-duct of the L-1011 Tristar. Fooot's answer shows a cut-out of the L-1011. Looking at this cut-out, I'm wondering: If the engine is at the 'normal' location of the APU, ...
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How much electrical power is available in a Gulfstream G550 and from which power sources?

I'd like to understand what electrical power sources are available (engines? APU? GPU? Other?) on a larger jet like the G550, and how much power they can provide, depending on whether the airplane is ...
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When do commercial flights turn off the APU?

On commercial flights do the pilots ever turn off the APU? Is it needed when flying?
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Can airliners operate without an operating APU?

As the APU (Auxiliary Power Unit) can be turned off when the engines are running, a functional APU may not be needed given you are able to start at least one engine. This question is in two parts: Is ...
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What could cause the APU on a Boeing 777 to fail and also trip the GPU?

I am a cargo aircraft loader at Heathrow and while we were offloading cargo, pallets and baggage containers from a Pakistan Airlines B777, the aircraft's Auxiliary Power Unit (APU) failed. It made ...
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What prevents aircraft with a tailcone APU from using tail-mounted airbrakes?

The BAe 146 and Fokker F-28, which are virtually alone among jetliners in lacking thrust reversers, compensate by using large, tail-mounted airbrakes to help slow the aircraft during descent and ...